It works when you do not use quotation marks -- the matching terms in the short snippet of text from the website ARE bolded in that case?

I don't know why the results would be different with quoted text.

Any difference if you first search without quotes, then click Ferramentas to open the Tools drop-downs. Then click "Todos os resultados" and click "Ipsis Verbis"?

I only mentioned the quote search as this is usually the term(s) that interests me primarily within the search results.

The search results also do not appear when I don't use quotes.

Maybe it is one of Google's experiments. I don't have an explanation.

You could also try clearing the web cache in case a mismatched style sheet or script file is the problem: How to clear the Firefox cache.